If you've ever taken a bus, you've probably found someone sleeping in the seat near you. Maybe this even happens to you. You might think you need more coffee, but it won't help much. The natural vibration(振动) of buses and subways makes us feel sleepy, accordin...
We've talked about snails(蜗牛) and their slow move. But much of the time snails don't move at all. They are in their shells(壳)--sleeping. Hot sun will dry out a snail's body. So at the least sign of hot sun, a snail draws its body into its shell. A...